This invention relates to construction members and is particularly concerned with structures of the type where interconnecting construction members support a fabric or film skin. The invention is particularly concerned with novel structural support members, or ribs, and methods of making them.
Fiber-reinforced plastics (hereinafter, "FRP") are well known as construction materials, specifically beams, ribs, bars, posts, rods, etc. These composites are widely used in industrial and automotive applications. Various fibers, including glass, carbon, nylon, polyester, and Kevlar.RTM. fibers, have been developed for use in FRP. These fibers have been used in various forms, including filaments, yarns, mats, woven roving, and chopped strand. The strength of the fiber is utilized through the transmittal of load by a resin. Common resins used are vinyl ester, polyester and epoxy resin. Present practice includes the concurrent application of resin and fiber in forming FRP materials.
Current practice teaches various methods of producing and shaping FRP into beams, ribs and the like. Most current methods include use of a mold to form sections of FRP. In some commercial structures, elongated rigid ribs are formed from FRP by pultrusion, extrusion, injection molding, progressive molding, press molding, or contact molding. In most domed structures, ribs, extending radially from a central rib, are formed of hinged sections, so that the dome is not smoothly curved. These domed structures are used as covers for swimming pools, municipal sewage digesters, etc. Current contact molding practice utilizes a standard set of molds, e.g. "small", "medium", and "large", to construct building roofs entirely of FRP. In, for example, domed structures, triangular-shaped sections of FRP, with ribs as reinforcing means incorporated within the FRP sections, are used. Both the rib and "skin" are of FRP. One longitudinal edge of these FRP sections, being a relatively smaller rib, interconnects with the adjoining FRP section forming a hinge, the larger rib overlapping the relatively smaller rib thus doubling the rib and increasing the load resistance of the structure roof but also increasing the expense of producing the roof.
In arched structures, ribs generally extend in paired fashion from a central "ridge pole." Again, where the entire roof is of FRP and the ribs interconnect in similar fashion, a large quantity of FRP is utilized. Presently, a standard set of molds is used to avoid the considerable expense of custom-sizing these structures. As a result, the final arcuate structure may be larger than necessary, resulting in the use of excess material and increased cost.
A further shortcoming of the existing technology is the shipping constraint preventing overland transport from exceeding 11 feet widths. While it is not impossible to transport items exceeding 11 foot widths, it is much more expensive to do so. With dome construction, the triangular-shaped FRP sections, the longitudinal sides thereof being the rib support radiating out from a central hub, the lateral edge or edge opposite the hub between the longitudinal edges, can be no wider than 11 feet for economical overland transport. Additional sections are sometimes required because, although larger sections would be adequate to support the load, the sections would be too wide to be economically transported overland. Therefore, the individual sections must be manufactured in smaller width dimensions to allow for economic overland transport, increasing the number of sections and increasing use of FRP in manufacturing the interconnections.
For the foregoing reasons, there is a need for structural support members that can be custom-sized, more economically produced because they minimize the use of construction materials, and more economically transported because they do not exceed the 11 foot width limitation.